This invention relates to dental compositions and, more particularly, to foamable fluoride compositions which are adapted to provide stable foams for use in dental therapy.
It is generally understood in the dental art that certain kinds of food decay are initiated by acid etching of the tooth enamel with the source of the acid being a metabolite resulting from bacterial and enzymatic action on food particles in the oral cavity. It is generally accepted that plaque--which is a soft accumulation on the tooth surfaces consisting of an organized structure of micro-organisms, proteinaceous and carbohydrate substances, epithelial cells, and food debris--is a contributory factor in the development of various pathological conditions of the teeth and soft tissue of the oral cavity. It has been suggested that the saccharolytic organisms of the oral cavity, which are associated with the plaque, cause decalcification beneath the plaque matrix through metabolic activity which results in the accumulation and localized concentration of organic acids. The etching and decalcification of the enamel may continue until the pulp chamber of the tooth is reached.
Fluoride compounds have been incorporated into dental topicals and into consumables to provide an orally beneficial effect by reducing the dissolving action of acids on dental enamel. It has been reported that the fluoride combines with hydroxyapatite, the crystalline structure of the teeth, to produce a modified crystalline structure which is more resistant to acid attack.
Diverse fluoride compounds have been disclosed in the prior art for use in dental care including, for example, sodium fluoride, sodium monofluorophosphate, stannous fluoride, fluoroalkyl phosphates, and quaternary ammonium fluorides.
The fluorides can be incorporated into gels, rinses, toothpaste, tooth powder, chewing gum and the like for topical application. Fluoride treatment can also be undertaken through consumables such as fluoridated drinking water and fluoride tablets. Heretofore, fluoride gels have been used in dental practice to topically apply fluoride to the teeth. The fluoride gel is usually supplied as a thick gel in a plastic bottle from which it is dispensed into the trough of a plastic dental tray that is inserted into the mouth in juxtaposition to the teeth whereby the teeth engage the gel for about 1 to 4 minutes, as per the supplier's instructions.
A typical fluoride gel contains water, a water soluble dental fluoride such as sodium fluoride, glycerol, an acidifying agent such as phosphoric acid, and a water soluble thickener such as carboxymethyl cellulose, polyvinyl alcohol, or xanthan gum.
An illustrative fluoride gel formulation is as follows:
______________________________________ INGREDIENTS PARTS BY WEIGHT ______________________________________ Water 85.5 Sodium fluoride 2.7* Xanthan gum 3.2 Glycerol 3.4 Phosphoric acid (85%) 4.1 ______________________________________ *Available fluoride 1.2 pts. by wt.
The water soluble thickener is selected so as to provide a highly viscous and thick system for maintaining the gel in the tray and in positive contact with the teeth, since a thin gel would tend to flow away from the tooth surface and thereby reduce fluoride uptake by the tooth and, additionally, a thin gel could flow out of the tray and cause the patient to gag and choke.
The acidifying agent is selected so as to provide the fluoride gel with a pH between about 3.0 and 4.5 which facilitates and enhances fluoride uptake by the teeth.
There are several problems associated with the use of fluoride gels in dental therapy. One of the most vexing problems is that of viscosity. The fluoride gel must be thick enough so that it does not flow out of the dental tray while the tray is in the patient's mouth and, at the same time, the gel must be thin enough to be dispensed from a plastic bottle into the tray in preparation for the fluoride treatment. Because it is extremely difficult to formulate a fluoride gel that flows from a plastic dispensing bottle and yet remains stationary in the dental tray for up to 4 minutes while in the mouth, the fluoride gels heretofore available had a tendency to flow while in the tray and cause patient gagging during the course of treatment.
Another problem associated with fluoride gels is that of toxicity. Fluorides have a low concentration threshold for exerting toxic effects. It is reported that severe symptons can be manifested from the ingestion of less than one gram of sodium fluoride. Thus, the ingestion of any significant amount of fluoride gel can produce serious consequences. This risk is especially noteworthy because fluoride gels, which have been flavored to mask the acidic taste, are most often used to treat children and the flavoring can increase the chance of unintentionally swallowing a significant amount of the semi-fluid gel.
A further problem associated with fluoride gels is the cost-effectiveness of the thick gel. In view of the high viscosity of the fluoride gels, the only fluoride which is available for uptake by the tooth is that which is in the immediate vicinity of the tooth surface. The remaining fluoride, which is the bulk of the fluoride in the tray, is unavailable for dental uptake because fluoride movement is restricted by the high viscosity of the gel.
Accordingly, it would be advantageous to provide a tray-fluoride that is non-flowable and which requires substantially less fluoride in the tray to achieve the same fluoride uptake as a corresponding volume of fluoride gel.